1. Field of the Invention
The present invention described in the present specification relates to a technique to support bi-directional communication using transmission/reception of moving images.
The invention proposed by the inventor has aspects of a communication system, a terminal apparatus and a computer program.
2. Background Art
In a TV conference system in a digital line in related art, ISDN is used as the communication line. In the ISDN, communication bandwidth is guaranteed. Accordingly, the communication rate is constant, and data loss hardly occurs.
However, in recent years, instead of the ISDN with a narrow bandwidth, the use of an IP (Internet Protocol) based Internet network is being rapidly increased as the communication line.
In ADSL (asymmetric digital subscriber line) or optical line using the Internet network, there is provided a best-effort service in which the bandwidth is not guaranteed (hereinafter, a network in which this kind of service is provided will be referred to as a best-effort network). However, in this kind of network, the communication state varies from hour to hour.
Thus, there is a possibility that a packet loss due to congestion or a bit error occurs.
As a result, damage, disturbance, skip and the like occur in the transmitted image and audio data.
In addition to this, in the Internet network, the channel quality of the uplink and the channel quality of the downlink do not generally coincide with each other.
Thus, in a TV conference system or a TV telephone system in related art, there can arise a state where although an image is received without loss at one side, it can not be received at all at the other side.
In this case, the user A whose reception state is excellent does not notice the state of the user B whose reception state is unstable, and continues the conversation in a unilateral way, and after a while, he/she notices the state of the opposite party.
Then, there is proposed a contrivance in which the occurrence of a communication abnormality on the transmission path is detected, and is notified to the user A whose reception state is excellent.
[Patent document 1] JP-A-2005-210160